It includes the grsync graphical application. If you only want rsync, you better use pkg for now:

pkg install rsync

Since this is a command line application, maybe Jason thinks no separate service should exist. But it is possible to create a non graphical service for rsync. But probably it needs a panel interface for people to work with it. Without such a panel interface, it remains a command line application. And for people working on the command line, the above command is probably not all that bad and actually faster than installing a ZFSguru service.

Yes, I thought about integrating rsync directly in the web-interface. For now, the service might actually be usable to novice people since the graphical application (grsync) allows them to learn rsync without reverting to the command line with its steep learning curve.

It is assumed that people like yourself who use rsync on the command line, would be knowledgeable enough to install it themselves. With the 'pkg' command this is really easy, as CiPHER demonstrated.

But I am open for suggestions; should there be a regular (non-X) rsync service?

I am looking for this functionality, too. It is in my opinion a little weird when controlling your server through the web interface you need to install gnome. In that case one could just use remote desktop to control the server, right? Correct me if I am wrong, but when one installs the command line rsync on the server side, one could simply control it from the client side with a GUI on rsync there? If that's not the case, is configuration of the server side rsync difficult? When I need to change permissions through the terminal it would be too difficult for me, I fear... If someone has it working I kindly ask to share the knowledge, though. Also, integrating the rsync command-line version in the web GUI would be very useful I think!